1. Field of the Invention
The present invention relates to a control circuit for driving a transducer that is coupled to a mechanical cutting element.
2. Prior Art
The lens of a human eye may develop a cataracteous condition which affects a patients vision. Cataracteous lenses are sometimes removed and replaced in a procedure commonly referred to as phacoemulsification. Phaco procedures are typically performed with an ultrasonically driven handpiece which is used to break the lens. The broken lens is removed through an aspiration line that is coupled to the handpiece.
The handpiece has a tip which is inserted through an incision in the cornea. The handpiece typically contains a  number of ultrasonic transducers that convert electrical power into a mechanical oscillating movement of the tip. The distal end of the tip has an opening which is in fluid communication with the aspiration line. The oscillating movement of the tip will break the lens into small pieces that are then drawn into the aspiration line through the tip opening.
The handpiece is typically connected to a console that contains a power supply. The power supply provides a driving signal that drives the ultrasonic transducers. To obtain a maximum response from the ultrasonic transducers, the frequency of the driving signal is typically at, or close to, the natural frequency of the transducers. A driving signal at the natural frequency will cause the transducers to operate in a resonant mode.
It has been found that an ultrasonically driven tip will generate heat which may burn or otherwise denature the corneal tissue. The denatured tissue may affect the patients vision. Additionally, the oscillating tip creates turbulence in the surrounding fluid. The turbulent fluid can make it difficult to view the end of the tip and increase the difficulty of performing the procedure. It  would be desirable to provide an ultrasonically driven handpiece that can cut tissue but does not generate a significant amount of heat. It would also be desirable to provide a phaco handpiece that does not create a relatively large amount of turbulence during operation. 